Note: Descriptions are shown in the official language in which they were submitted.
CA 02313853 2000-07-11
REFLECTIVE LASER COLLIMATOR
Field of the Invention
The present invention generally relates to a family of devices known as
collimators or telescopes, which increase or decrease the size of an input
light
beam and more particularly relates to a servo controlled reflective collimator
for adjusting the divergence of a high power laser beam in a beam path of a
laser-equipped machine tool such as laser cutting machine or laser welding
machine.
Background Of The Invention
Collimators are optical devices, belonging to a family of devices
known as collimal:ors or telescopes, which include products called beam
expanders and condensers. Such devices, advantageous to the laser-equipped
machine tool industry, increase or decrease the size of and change the
divergence or angular characteristics of a light beam passed through it. Such
devices also have other characteristics and functions known to those skilled
in
the trade. Manufacturers of laser optics publish literature providing
information on design variations and examples of use, for example: II-IV
Incorporated publication 1685 Revised 3/92, Beam Expander-Condensers,
Copyright 1988.
Collimators may be constructed of transmissive optics such that the
light beam is passed through the optics. They are commonly used in laser
equipped machine tools up to the approximately three kilowatt power level
and sometimes above. Use of transmissive collimators with lasers with power
levels above three kilowatts becomes increasingly problematic due to limits
on energy density that transmissive optic materials can withstand and due to a
CA 02313853 2000-07-11
2
phenomenon called thermal Tensing. Thermal Tensing is the distortion of an
optical component caused by heat absorption typically from an input beam of
light. The distortion can influence the divergence and mode quality of the
beam passing through or reflecting from the optical component and cause
S detrimental shifts of focus position and diameter.
Collimators are also constructed of reflective optics, combinations of
flat and shaped mirrors, such that the light beam is reflected from these
optical
elements. Reflective optical materials can withstand greater energy densities
without damage and thermal Tensing is not as severe in reflective optics as
compared to transmissive optics. Thus reflective collimators are more
suitably used in high power laser applications.
Known reflective collimators consist of four reflective optics. By
adjusting the distance between specific optics the divergence of the output
beam can be varied. U.S. patent 5,442,436 illustrates such a system as does
II-VI Incorporated sales literature "Model RBC-Dx Reflective Beam
Collimator" dated September 1992. The mirrors are arranged in pairs in
parallel planes. 7'o change the size of the output beam one pair of mirrors is
moved parallel to the input and output beams and the distance between the
pairs is changed.
~ It is advantageous to reduce the number of optical components used in
the beam deliver3~ system. Each optic adds complexity to the task of aligning
a beam path, is a possible source of beam distortion and absorbs some energy
from the beam reducing overall system efficiency. Optical elements degrade
with use. Each optical element adds to the overall cost of system
maintenance.
Summar~r Of The Invention
In view of the foregoing, it is a general aim of the present invention to
CA 02313853 2000-07-11
3
reduce the numbe:r of mirrors in an adjustable reflective collimator.
In that regard, an object of the present invention is to provide a
reflective collimator having fewer optical elements, some of which are
mechanically linked so as to maintain optical alignment during relative
movement between minors and such that the divergence of the beam can be
changed by changing the position of a single adjustment mechanism.
An objective of the present invention is to produce a reflective
collimator with a reduced number of optical mirrors, in which a minimum
number of mirrors require movement for changing the size, divergence, or
collimation characteristics of a beam and such that the characteristics can be
changed by changing the position of a single adjustment mechanism.
It is a more detailed object to provide a three mirror reflective
collimator in which movement of only two of the minors is necessary to
adjust beam characteristics, with the moving minors being connected by a
1 S linkage which precisely maintains optical alignment through their range of
movement and such that the output beam divergence can be changed by
changing the position of a single adjustment mechanism.
A further object is to provide such a collimator which is suitable for
adjustment under the control of a single servo control system.
It is another object of the invention to provide a collimator in which a
single servo motor adjusts the beam characteristics with a mechanical linkage
utilized to maintain optical alignment between two moving mirrors moving in
non-parallel axes.
In a broadf;r view, it is an object of the present invention to provide a
robust and reliable collimator, so as to allow adjustment of beam
characteristics in a continuous manner as conditions change which may
require the alteration of the beam characteristics, and which utilizes two
mirrors, mounted to move on non-parallel axes and connected by a linkage to
CA 02313853 2000-07-11
4
precisely maintain their optical alignment.
It is a feature and an advance of the invention that reliable adjustment
of beam characteristics can be achieved using only two translatable mirrors,
with the optical geometry changed by movement of the mirrors connected by
a mechanical linkage, precisely translating one mirror, slideably mounted in a
non-parallel axis relative to the other moving mirror, in response to movement
of the other moving mirror which is a slideably mounted driven mirror. In its
currently preferred form, a third fixed mirror is utilized because it provides
sufficient flexibility to reduce the overall size of the machine in which the
collimator is used.
It is a further feature of the invention that a reflective collimator is
provided in which the beam path through the collimator defines a triangular
geometry, and that two mirrors, mounted on non-parallel axes translate, along
the beam path, for adjusting beam characteristics and are connected by a
linkage including a pivotable coupling having a triangular geometry
proportional to the triangular beam path geometry.
It is a further feature of the invention that only a single servo system is
required to drive the collimator, with a robust and reliable mechanical
linkage
interconnecting movable mirrors, so that the collimator can be controlled by
the Computer Numerical Control which controls a laser-equipped machine
tool and continuously adjusts the beam characteristics as the beam delivery
head traverses the; workpiece and as the beam characteristics change due to
changes in laser power.
Other objects and advantages will become more apparent from the
following detailed description when taken in conjunction with the
accompanying drawings.
CA 02313853 2000-07-11
Brief Description Of The Drawings
FIGURE 1 is a plan view of a collimator exemplifying a preferred
embodiment of the present invention;
S FIG. 2 is a partial view of the collimator in elevation, with the
enclosure removed, taken along the line 2-2 of FIG. 1;
FIG. 3 is a partial sectional view, in elevation, with the enclosure
removed taken along the line 3-3 of FIG. 1;
FIG. 4 is a partial view of the area within the dashed circle 4 of FIG. 2,
showing the details of a preferred form of preloaded joint used in the
mechanical linkage of the collimator;
FIGs. 5, 6 and 7 are diagrams of the optical elements of the collimator
of FIG. 1 showing the effect on beam divergence achieved by differently
adjusted positions of the collimator;
FIG. 8 is a diagram similar to FIG. 5 but illustrating important angular
relationships in the beam path geometry of the collimator of FIG. 1;
FIG. 9 is a diagram similar to FIG. 5 but illustrating important
relationships between the beam path geometry and the linkage which operates
the linearly translatable mirrors; and
FIGs. l0a and l Ob are diagrams schematically illustrating beam path
geometry and the associated coupling linkages for alternative embodiments of
the invention.
Detailed Description Of The Preferred Embodiments
While the invention will be described in connection with certain
preferred embodiments, there is no intent to limit it to those embodiments. On
the contrary the intent is to cover all alternatives, modifications and
CA 02313853 2000-07-11
6
equivalents as arc: included within the spirit and scope of the invention as
defined by the appended claims.
The follovving description will proceed to first identify the mechanical
and optical elements of the collimator and their physical locations, then to
examine the beam path through the collimator, then to describe how
collimator adjustment alters the beam divergence, then to describe the details
of the mounting arrangement and linkage which operates, according to the
present invention, to adjust beam divergence. Alternative beam
configurations will be described to illustrate the breadth of the invention.
With that in view, attention will be directed to FIG. 1 supplemented by
FIGs. 2 and 3. FI:G. 1 shows parts of an enclosure 60 used to house the
collimator generally indicated at 21. The enclosure 60 includes a base plate
61 which is the support for the optical elements of the device, all of which
are
supported so that the optical axes are in a single plane. The input port 51
includes a coupling 63, shown only schematically, for connection to the
output port of a laser, to seal the beam path. The output port 52 has a
schematically illustrated coupling 53 to seal the output beam path for
connection to the remainder of the beam delivery system of a machine tool.
The preferred collimator of FIG. 1 includes three precision optical
~ mirrors. The laser source projects a beam through input port 51 which is
reflected by first mirror 65 to a second mirror 66. The second mirror, 66, in
turn is angled to reflect the beam to a third mirror 67 which thereupon
reflects
the beam to the output port 52. The alignment and relative positioning of the
mirrors is precisely established in the collimator to assure that beam
propagation axis coincides with the minor centers. In the preferred
embodiment the input mirror 65 is a zero phase shift piano (flat) mirror,
although it could be a quarter-wave phase retarding circular polarizing
mirror.
CA 02313853 2000-07-11
7
The second mirror 66 is convex, and the third mirror 67 is concave. The
second and third mirrors make up a mirror pair with curved, reflective
surfaces, which cooperate to adjust beam divergence, as will be described.
The beam path th~.-ough the collimator is illustrated by the dashed center
line
which projects through the input port S l, a first beam element 70 being
directed from the input port to the first mirror, a second beam element 71
being directed from the first to the second mirror, a third beam element 72
being directed from the second to the third mirror, and a fourth beam element
73 being directed from the third mirror to the output port 52. Adjustment of
the length of the beam element 72 will be used in the illustrated embodiment
to adjust the divergence of the collimated output beam.
In the illustrated embodiment the third mirror assembly 76 is fixed to
the base 61, so that it cannot and need not move during the adjustment
operation. As best seen in FIG. 2, the mirror assembly 76 is made up of a
mirror mount 75 which has a high quality optical mirror 67, preferably metal
and usually copper, carried within the holder 77, and configured with
apparatus 77a at tile back of the mirror holder 77 adapted to pass a coolant
through internal passages in heat exchange relationship with the mirror to
prevent excessive temperature rise of the mirror. The mirror mount 75, which
could be bolted directly to the base, in the illustrated embodiment is
preferably constructed with a straddle bracket 75a which straddles a servo
motor 78. The purpose of the servo motor will be described below. The
mirror mount bracket construction 75a allows the mirror mount 75 to be
affixed directly to the base as by bolts 79, while allowing room for the servo
motor 78 to be folded back within the configuration to reduce overall
collimator size.
In the preferred embodiment, the other two mirrors, namely mirrors 65
and 66 are linearly translatable over predetermined non-parallel axes. The
CA 02313853 2000-07-11
manner in which that is accomplished will first be described in connection
with intermediate mirror 66. Referring again to FIGs. 1, 2 and 3, it will be
seen that mirror assembly 80 includes a mirror mount 80a, which has a high
quality optical mirror 66, preferably metal and usually copper, carried within
the holder 80b. The minor 66 is fitted with coolant conveying elements 82
for supplying cooling fluid to passages internal to the minor to prevent
excessive temperature rise of the mirror. The mirror mount 80a is fixed to a
slide plate 83 which can translate along a base 86 of a slide assembly 84. In
the preferred embodiment, in order to assure the precision and accuracy
desired in this application, a precision optical slide, which is a
commercially
available component, is utilized. Simpler configurations, with less
restrictive
accuracy demands, can use more conventional way and slide type structures.
The optical slide assembly 84 of the illustrated embodiment, utilizes an
internal ball screw, rotated by an input shaft 85. The ball screw rides in a
ball
nut (not shown) which is coupled to the slide plate 83 to cause the slide
plate
to be driven in very precise measured amounts along base 86 (see FIG. 1).
Preferably the internal working elements are covered by a bellows 87 for
protection.
The previously mentioned servo motor 78 has its output shaft 88
connected by a coupling 89 to the input shaft 85 of the slide assembly 84. The
servo motor has electrical connections 90, 91 for power and feedback
respectively. Those connections can be brought back to a programmed CNC
controller for operating the servo motor which in turn drives the mirror 66
along its slide. It will be appreciated from FIG. 1 that the slide assembly 84
is
precisely aligned with the portion 72 of the beam path which is directed from
the second to third mirrors. Thus the mirror 66 will be moved toward or away
from the mirror 6'7 while maintaining optical alignment between those
elements.
CA 02313853 2000-07-11
9
The input mirror 65 is also preferably mounted on an optical slide
assembly 94 whit;h includes a base 95 fixed, via spacer block 95a, to the base
61. The base 95 of the optical slide assembly 94 carries a slide plate 96 to
which is mounted. mirror assembly 97, which includes a mirror mount 97a,
which has a high quality optical mirror 65, preferably metal and usually
copper, carried within a holder 98. The minor 65 is fitted with coolant
conveying elements 98a for supplying cooling fluid to passages internal to the
mirror to prevent excessive temperature rise of the mirror. It will be seen
from
FIG. 1 that optical slide assembly 94 is arranged to translate the slide plate
96
and mirror 65 along the element 70 of the beam path.
For completeness, it will be pointed out that FIG. 1 illustrates the
coolant flow in which an inlet port 100 conveys coolant to the system which is
piped by a first tube section 101 to the first mirror, and, after passing
through
passages associated with that first mirror, through a second tube section 102
to
the second mirror, and, after passing through passages associated with that
second mirror, through a third tube section 103 to the third mirror, and,
passes
through the associated third minor apparatus whereupon a fourth tube section
104 conveys the fluid to a coolant output port 105. A separate port 106 is
provided for input of purge gas, in the preferred embodiment specially
scrubbed air, to maintain the inside of the collimator enclosure at a slightly
elevated pressure to prevent ingress of contaminants or those components of
dried-filtered air undesirable in the beam path. As noted, the enclosure for
the
collimator is tightly sealed, and the scrubbed air through the port 106
further
assures the cleanliness of the internal elements.
FIGs. 5, 6 and 7 are simplified schematic drawings of the preferred
embodiment of the invention, and illustrate the translation of the movable
mirrors to adjust output beam divergence. The mechanism for performing the
adjustment will be shown later. The input beam path 70 is shown at the center
CA 02313853 2000-07-11
of an input laser beam 110 and is incident on the piano mirror 65. A reflected
laser beam 11 l, of roughly the same size and shape, is centered on the beam
path element 71, .and is incident on the convex mirror 66. The relative
positions of the centers of curvature of the curved mirrors 66 and 67 will
5 determine the amount of divergence of the output beam.
In the FIG. 5 illustration, the slide plates 83, 96 are in their middle
separation distance position, to produce a collimated output beam with
minimum divergence. The mirror 67 is concave in shape, with the shape
coordinated to thc; convex shape of the mirror 66, so that, at the center
position
10 mirror separation., the diverging beam which impinges on mirror 67 is
converted to a roughly parallel collimated output beam.
In the FIG. 6 illustration, the slide plates 83, 96 are in their largest
separation distance position, to produce an output beam with negative
divergence or a converging output beam. The mirror 67 is concave in shape,
with the shape coordinated to the convex shape of the mirror 66 such that,
when the mirror separation is greater than that at the center position in FIG.
5,
the diverging beam which impinges on the concave mirror 67 is converted to a
converging output beam.
FIG. 7 shows the opposite extreme of adjustment of the collimator in
~0 which the slide 83 is adjusted so that the mirror 66 is in its closest
relative
position to the mirror 67. In this adjusted position, an output beam is
produced with maximum divergence. The mirror 67 is concave in shape, with
the shape coordinated to the convex shape of the mirror 66 such that, when the
mirror separation is less than that at the center position in FIG. S; the
diverging beam which impinges on mirror 67 is converted to another
diverging output beam.
It will now be appreciated that relative adjustment of the mirror 66
along the axis established by the slide on which it is mounted can be used to
CA 02313853 2000-07-11
11
continuously vary the divergence of the collimated beam between the limits
established by the; travel. It will now also be appreciated that the servo
motor
78 discussed above drives the ball screw of the slide assembly 84 to translate
the slide plate 83 along the slide axis to thereby achieve the continuously
variable beam divergence adjustment described above.
In accordance with the invention, a linkage is provided between the
relatively movable mirrors in the collimator in order to maintain optical
alignment through the collimator as the adjustment for beam divergence,
described above, is accomplished.
Thus, in the illustrated embodiment, the positions of the input and
output segments of the beam path, namely segments 70 and 73, remain
constant, and the mirror 66 translates along the beam path 72, which likewise
remains constant in position. However, in order to maintain optical alignment
between the elements in that arrangement, the beam path 71 must translate as
1 S the mirror 66 translates. With that being accomplished in accordance with
the
invention, optical alignment is maintained throughout the adjustment range.
Alignment is maintained by causing the mirror 65 to translate along its
optical
slide assembly 94 in proportion to the movement of the mirror 66 along its
optical slide assembly 84. Thus, comparing FIGs. 6 and 7, it will be seen that
with the mirror 6f> in its substantially extended position (toward the bottom
of
the drawing in FIG. 6), the minor 65 is in a substantially rearward (to the
left)
position, so that the beam element 71 alignment is maintained between the
centers of the respective mirrors. Comparing FIG. 7 to FIG. 6, it will be seen
that the mirror 65 is translated to the right, to bring the beam path 71 to
the
right of the position illustrated in FIG. 6, although parallel with that
position,
to maintain alignment between the center of minor 65 and the newly adjusted
position of the translatable mirror 66.
CA 02313853 2000-07-11
12
The significance of the linkage which maintains alignment will be
better illustrated with reference to FIG. 8 which illustrates the geometry of
the
beam path in the center or "reference" position of FIG. 5. In that position,
the
beam path elements create a triangular geometry which is replicated in the
linkage to cause :movement of the translatable mirrors in unison while
maintaining optical alignment. Thus, it can be seen that the beam element 71,
which joins the centers of the mirrors 65 and 66 forms one side 131 of a
triangle 130 which in this case is a right triangle. The beam path 70, when
extended, forms a second side 132 and the beam path 72 when extended as
illustrated forms a third side or hypotenuse 133. Thus the triangle 130 having
sides 131, 132, 133, forms a triangular pattern in the beam geometry which is
replicated in the linkage.
The incidc;nt and reflected beams on mirror 67 form an angle a2. This
is shown in FIG. 8 by the beam path element 72, 73 and the included angle a2.
Since the slide 83 is aligned with the beam path 72, the angle a2 remains the
same in this collimator. The beam paths incident and reflected on mirror 66,
namely beam paths 71, 72, form an angle a, as also shown in the drawings.
The angles al and a2 must be chosen specifically to minimize distortion of the
output beam after. reflection from curved mirrors. The relationship between
those two angles is determined by the magnification of that portion of the
optical system. That relationship can be expressed mathematically as:
2
a,
- .
(mag .)
Thus, if a magnification of 2 is desired, a definite relationship is
established
between the two ;angles. Considering the matter in another way, however, if
during adjustment of output beam divergence, one of the angles changes with
respect to the other, an undesirable effect on output beam quality is
obtained.
CA 02313853 2000-07-11
13
Thus, with oc2 fixed, it is an object of the linkage to maintain a, also
fixed,
thereby to maintain alignment, and prevent distortion in the optical system.
It can therefore be seen that, to maintain the correct alignment between
the mirrors, mirrc>r 65 must travel a distance proportional to the distance
traveled by mirror 66 such that angle a, remains constant. Following from the
basic system geometry, the proportion which mirror 65 must move, in relation
to mirror 66, is represented by the relation of the lengths of the short side
132
of triangle 130 anal the hypotenuse 133 of triangle 130.
In accordance with the invention, a linkage is provided for
interconnecting the translatable mirrors, the linkage having a three point
pivot
coupling, with the points of the pivot coupling establishing a triangle which
is
proportional to the beam geometry triangle 130. The location of the linkage
may be translated with appropriate couplings to allow for a variety of
locations in various implementations of the invention. It is necessary only to
preserve the correct geometry. In the preferred embodiment, the linkage is
implemented above the beam path to simplify the alignment and to provide a
mechanism which reduces any off axis forces which may tend to cause
misalignment of the mirrors during adjustment. In the FIG. 9 embodiment,
the linkage geometry is illustrated in the center or reference position. The
pivotable coupling is illustrated at 140. The coupling 140 has three pivot
points 141, 142, 143; connecting the pivot points forms a triangle 144 similar
to triangle 130, and therefore having proportional sides and equal angles.
Thus, the hypotenuse of the triangle 130, illustrated in FIG. 9 as having a
length B, has a proportionality to the hypotenuse 145 of the triangle 144,
illustrated as having a length B'. Similarly, the short side of the triangle,
illustrated as having a length A, has a proportionality to the short side 146
of
the triangle 144, illustrated as having a length A'.
CA 02313853 2000-07-11
14
In the FIG. 9 embodiment, the pivot point 141 is located above the leg
132 of the triangle 130. A link 147 is then provided and is connected between
the pivot point 141 and a pivot point 150 directly above the beam path on the
mirror mount 97a for the mirror 65. The second pivot point 142 of the pivot
S coupling 140 is fixed with respect to the base of the collimator. Turning to
FIG. 3 briefly, it will be seen that the pivot point 142 in the pivot coupling
140
is affixed at 150a. to an upstanding rigid column 151 which in turn is affixed
at
152 to the base plate 61.
In practicing the invention, the third pivot point 143 of the pivotable
coupling 140 is connected by a pivotable link 148 to a further pivot point 149
directly above the beam path on the mirror mount 80a which carries the
translatable mirror 66. The pivotable links 147 and 148 are conveniently
configured with right hand and left hand threads and jam nuts in the
respective
knuckle elements thereof so that the link can be adjusted precisely to its
desired length and the jam nuts tightened to establish the lengths of the
links
and the geometrical relationship between the beam path triangle 130, the pivot
coupling triangle 144, and the links which connect the coupling to the mounts
of the translatablE: mirrors.
Since the length A of the beam path triangle 130 is proportional to the
length A' of the pivot triangle 144, and since the length B of the hypotenuse
of
the beam path triangle 130 is proportional to the length B' of the hypotenuse
145 of the pivot coupling triangle 144, the following proportionality is
established:
_A' _B'
A B
Rearranged this leads to the relationship:
_A _A'
B B'
CA 02313853 2000-07-11
When the collimator is adjusted, the coupling pivots about pivot point 142.
The distance that pivot points 141 and 143 travel will be proportional to the
distance between each pivot point, 141 and 143 respectively, and the point
142 about which 'they pivot. This may be seen from the following equation
5 describing the distance traveled "d" around the edge of a circle being equal
to
the angle moved "8" (in radians) multiplied by the radius of the circle "r":
d = r ~ 0
Referring to FIG. 9, as both pivot points 141 and 143 are on the pivot
coupling they must each pivot around pivot point 142 by the same angle of
10 travel through which the pivot coupling rotates. Therefore, as the angle of
rotation is the same for each pivot point 141 and 143, then the distance that
each pivot point travels must be proportional to each radius of rotation. The
radius of rotation for pivot point 141 is the distance A'. The radius of
rotation
for pivot point 143 is the distance B'.
15 In the illustrated embodiment, the length of the link 148 was selected to
correspond to the distance from the pivot point 143 to the approximate center
of the reflective surface of mirror 66. Referring to FIG. 9, for example, the
amount of rotation of pivot coupling 140 will increase per linear unit of
travel
of mirror 66 as the collimator is adjusted away from the center position.
A small movement of pivot point 143 near the center position, as
described in FIG. 9, will correspond to an almost equal amount of movement
of pivot point 149. The movement of pivot point 143, when near the center
position, is in nearly the same direction of travel as is pivot point 149 and,
as
these two points are connected by a link 148, which has a set length, then it
may be seen that both pivot points will travel nearly the same distance.
When the collimator is adjusted away from the center position, pivot
143 rotates around pivot 142 and thus the direction of travel of pivot point
143
is continuously shifted further away from the original direction of travel
near
CA 02313853 2000-07-11
16
the center position. Pivot point 149 continues in the original direction and,
as
pivot 149 and 143 are connected by link 148., pivot point 143 must pivot
further around pivot 142 to displace the necessary distance in the original
direction of travel.
S In other words, the amount of rotation of pivot coupling 140 will
increase per unit length of travel of minor 66 (including pivot point 149) as
the hypotenuse 145 of triangle 144 moves away from the original
perpendicular alignment with hypotenuse 133 of triangle 130. A similar
combination of movements will be seen occur .for the other linked mirror 65
and the associated pivot points 150 and 141.
To maintain alignment during collimator adjustment, the length C from
pivot 141 to pivot 150 is chosen to preserve the same proportion of angular
deviation for link 147 as exhibited by link 148. The relation of B' to B is
reproduced by the relation of A' to C such that:
B' A'
--- .
B C
It will be noted that the choice of length for link 148 to correspond to
length B
is not a necessary condition. The link 148, for example, can be coupled to the
carriage of mirror 66 at any point above the beam path 72, translating pivot
point 149, so long as the above proportionality is maintained by similarly
adjusting the length of the link 147 and the location of its pivot point 1 SO
above beam path 70.
In summary, when it is desired to increase the divergence of the output
beam, the servo drives the slide plate 83 to move the mirror 66 closer to the
mirror 67, in effect, shortening the length of the beam path 72. Movement of
the slide plate acts through the link 148 to pivot the coupling 140 about the
pivot center 142. In other words, the pivot point 143 swings upwardly about
the center 142 as the slide plate 83 is driven upwardly. That has the effect
of
pivoting the pivol: center 141 about the center 142 also in the
CA 02313853 2000-07-11
17
counterclockwise direction, causing the slide plate 96 to move to the right a
proportional amount. The coupling causes the movement to occur in
proportion which, in effect, translates the beam path 71 to the right while
maintaining that beam path parallel to its original position.
Recalling :from FIGS. 1 and 2 that a single servo motor can be coupled
to the slide plate 83 of the optical slide assembly 84, it will be seen that
simply controlling the position of the slide plate 83 which is a direct
control
over the output beam divergence, serves to operate through the linkage which
has just been described, to reposition the slide plate 96 to maintain beam
alignment throughout the geometry of the collimator from one adjustment
extreme to the other.
The linkage mechanism is not only theoretically correct in maintaining
the beam alignment according to the proportionality relationships described,
but it is also robust, which would allow the callimator to operate in real
time
to continuously adjust beam divergence and thus beam size at the cutting head
as the cutting head traverses the workpiece and as the laser power level
changes during normal operation. The pivot coupling itself is rigidly mounted
on an upstanding post so that it rides in the correct plane. The post 151 is
illustrated in FIGS. 2 and 3. It can readily be made sufficiently rigid.
There are love pivot points in the linkage, one on each of the slides, and
three on the pivot coupling. In the preferred embodiment, each of those five
pivot points is formed of a preloaded joint which is adapted to precisely
position the center without any radial play, and to provide long life under
relatively continuous operation. FIG. 4 illustrates, in enlarged form, one
such
pivot coupling. It will be seen that in the preferred embodiment the preloaded
joint 170 is made up of a drill bushing 171 which has a hard outer surface to
ride against a bearing, and a head 172 which allows clearance for the
pivotable member. A bolt 173, carrying a lock washer 174, passes through the
CA 02313853 2000-07-11
18
central aperture of the drill bushing 171 and is threaded into the pivotable
plate 140. Thus the bushing 171 forms a fixed pivot point for the element
which is to pivot 'thereon.
In the preferred embodiment, a needle bearing assembly 175 is press fit
on the outer diameter of the drill bushing, and fits closely within the inner
diameter of an apertured rod 176 which forms each end of the pivotable links
147, 148. Thus, the drill bushing serves as a pivot post about which rides the
needle bearing mounted rod, with substantially no radial play and smooth
guided movement as the mechanism pivots during the course of adjusting the
collimator. A bearing spacer 177 or thrust washer, such as of a plastic
material, is interposed between the pivot coupling 140 and the apertured rod
176. In the case of the preloaded joint which mounts the pivotable coupling to
the post 151, it will be understood that a further bearing assembly is
interposed between the pivot coupling 140 and the post 151 and that the pivot
coupling itself is pivoted about the drill bushing. Preferably each of the
five
pivot points is constructed as described in connection with FIG. 4 to provide
a
smoothly functioning unit.
The foregoing embodiment of the invention is currently believed to be
preferred, in part because it provides a reasonably compact structure.
However, it will now be apparent that other configurations are possible within
the scope of the invention.
Referring to FIGs. l0a and lOb, there are shown two additional
geometries which illustrate the breadth of the present invention. In the
configuration of the above described preferred embodiment, FIG. 9, the first
mirror is piano, the second mirror is convex, and the third minor is concave.
The intermediate mirror moves with respect to the third to adjust the beam
divergence, and the coupling causes the first mirror to track the movement of
CA 02313853 2000-07-11
19
the intermediate mirror to maintain beam alignment, all in accordance with the
proportionality described above.
FIG. l0a illustrates a similar geometry but folded in a somewhat
different fashion. In this case, an input laser beam 270 is first incident on
a
convex mirror 271 whereupon it is reflected to a concave mirror 272 and
thence to a piano or circularly polarizing output minor 273. The intermediate
mirror 272 is moved toward or away from the convex input mirror 271 in
order to adjust beam divergence. The triangular linkage, represented in the
drawing simply b;y triangular coupling plate 140', is linked to the
translatable
minors by links 272, 273 (illustrated by link portion near the pivot points,
but
with the link centers removed so that the beam path geometry can also be
illustrated). The i:riangular coupling plate with linkage causes the
appropriate
relative motion to have the mirror 273 track the position of the mirror 272 as
it
moves back and forth according to the direction of the slide 83' to adjust the
beam divergence.
FIG. l Ob il.lustrates a two minor embodiment of the present invention.
It demonstrates not only that it is possible to practice the present invention
with only two minors, but it also emphasizes the significance of the
subcombination of the two translatable mirrors in the three mirror
embodiments.
Thus, in FIG. lOb, an input laser beam 275 is incident on a first minor
which is shown in the drawing as a convex mirror 276. The reflected beam
277 is directed to a concave mirror 278 which produces an output beam along
a path 279. Output beam divergence is adjusted by adjusting the relative
position of the mirrors 276 and 278.
In the illustration of FIG. 9b, both mirrors 276 and 278 are mounted on
optical slides, 280 and 281 respectively, for linear motion in the direction
along the associated beam paths. A pivotable linkage, illustrated by
triangular
CA 02313853 2000-07-11
coupling 283 pivoted at 283a and links indicated generally at 284, 285,
establishes a proportionality between the beam geometry of the system and
the triangular coupling 283, to control the movement of the mirrors 276 and
278 with respect to each other. In this case the triangle established the beam
S geometry is the triangle 290 established by the beam paths 277, 279 and beam
path 275 extended as illustrated in FIG. lOb.
Thus, as mirror 276 translates downwardly to increase the output laser
beam divergence., the linkage will cause the mirror 278 to move downwardly
but a greater amount and on a different angle, so that the beam path 277
10 remains parallel to that shown in FIG. 9b, but is shorter so as to increase
beam
divergence. Similarly, when beam divergence is to be decreased, the minor
276 is translated upwardly, which acts through the linkage including coupling
283 to move the mirror 278 upwardly. The mirrors when moving upwardly
are moving such that the distance between them increases. As a result, the
15 beam divergence is decreased. The geometry including the mechanical
linkage and pivot coupling serve to maintain the beam path alignment
throughout this operation, and the collimator can be configured as a simple
two mirror system.
It will now be appreciated that what has been provided is a new
20 collimator geometry which requires only two translatable minors for
controlling output beam divergence. The mirrors are arranged to establish a
non-parallel single plane beam geometry which defines a triangle. A linkage
connects the two 'translatable mirrors and has pivot points arranged in a
triangle which is similar to the beam geometry triangle. Pivotable links
between the pivot coupling and the translatable mirrors are also in accordance
with the triangular geometry and proportionality of the triangles. Translation
of one mirror acts through the linkage including the triangular coupling to
CA 02313853 2000-07-11
21
translate the other mirror, thereby maintaining optical alignment in the
collimator while controlling output beam divergence.
